while i am for no trawling possible in patches and know that artificial reefs ( wrecks etc ) are good for fish breeding grounds it does seem a bit of a convenience to the rig owners to do a bit of scrub n tidy then put it out of sight using cutting charges to slice up the legs thus saving almost all of the costs of towing it away and dismantling it.

if they maybe paid half the scrapper costs into suitable environmental projects it would seem a win win win all round.

I'm a big fan of leaving some infrastructure in place after decommissioning an oil field in selected circumstances, precisely because of the artificial reef effect.

Before I start, it's important to understand that there are, simplistically speaking, two kinds of oil rig: those that float, and those that are support by the seabed. Those that float should, in all circumstances, be towed to a yard and dismantled responsibly at the end of their working lives. This includes mobile drill rigs of the kind discussed in the "where oil rigs go to die" (strictly speaking, these kinds of rigs aren't "oil" rigs anyway" - they are rigs that drill for oil but do not generally produce it).

For those that donít float, all equipment and structures above the water line (which generally represents tens of thousands of tonnes of steel) should also be removed and sent back to shore, along with anything near enough the surface to be a danger to shipping (unless the conservation aspects dictate otherwise, in which case access to the area should be restricted to prevent marine incidents).

A project I worked on in the North Sea some years back, and that shall remain nameless, was the first one that I am aware of that intentionally set out to study the artificial reef effect. Two years before anything man-made was put in place teams of divers were studying the full depth of the sea to perform what's nowadays referred to as a baseline environmental review, which is basically to understand the nature of the environment in which you'll be plonking your rig while that environment is still pristine. These divers reported several observations on the behaviour of marine wildlife that were new to science (but commonly observed by the amused deep-sea divers, who were all industry professionals Ė a special breed of person, if youíve never met one). The resultant rigs have been in place for a good few years now, and still have a long life ahead of them, but in-depth environmental reviews are periodically carried out and will continue to be carried out over the lifetime of the facilities so that the best decision can be made as to whether to completely remove all infrastructure on cessation of production or whether to leave some in place. The cost of removing and disposing of the jackets (the steel legs that the topsides stand on), although significant, is only a small proportion of the total cost of abandoning, decommissioning, removing and dismantling an installation, so I would expect the decision to be made primarily on an environmental rather than a cost basis.

Whilst Iíve not had any feedback on the artificial reef study of the facility I mention above, I have been following similar research that we do on our facilities out here, and have seen with my own eyes the artificial reef effect. There are very few items of note in the marine landscape out here, and although we do have fields of sea grass in the coastal shallows supporting a reasonable population of dugongs and a few small reefs dotted around here and there, the deeper waters further offshore are pretty barren (with the frankly awesome exception of one of the worldís largest agglomerations of whale sharks, but they come for the seasonal tuna eggs rather than anything more permanent). One of the biggest issues we have in our oil field is keeping the fishing boats (each one a potential ignition source should there ever be a gas release) out of our 500m zones. They come day in, day out for the lucrative pickings around our rigs in a Gulf that is being rapidly emptied of biomass by overfishing, covering up their registration marks so that the authorities canít track them down. They know theyíll more-than-likely lose their livelihoods, or at least face a steep fine if theyíre caught, but they come regardless as the fishing is the best in the region. Iíve seen with my own eyes the huge numbers of fish that call the jackets of our rigs home, and love visiting the cellar deck of one of our platforms in particular as it always has countless reef sharks lazily hanging in the water underneath it. When one of them bolts for a passing fish, the whole sea comes alive as enormous shoals of decent-sized fish make a swim for it. The only reason all these fish are here at all is because of the huge metal frames that have been pinned to the seabed over the past 25 years.

When our platforms have finally had their day, I will be a strong advocate for removing everything above the water line, but Iíll feel equally as strongly about leaving as much of the steelwork as possible below the water line, because to completely remove it would completely wipe out the ecosystem that has grown up and flourished here over the past quarter of a century.

It may sound like Iím looking at things through the rose-tinted glasses of somebody who earns his crust in the oil industry, but I look forward to the day that jobs like mine donít exist, and I hope it happens while thereís still a good proportion of todayís hydrocarbons still in the ground. In the meantime, in a world thatís going to use oil and gas regardless of who produces it or how, Iíll keep doing my little bit to make sure itís produced as sensitively as possible.

very interesting to read a greenish insider view, i had thought that a good scrub and removing the valuable bits before putting the whole thing on the sea bed might create the best "reef" but if most can be recycled and some left to produce a good habitat that might be even better.

on land "brownfield" sites such as demolished but still present mills etc do seem to create very rich and diverse ecosystems that are far more productive than the "pristine" areas around them. same goes for disused quarries if they are left as ragged holes rather than backfilled with rubbish.

ps i know a professional diver , they are a bit special even on dry land

In my view, just removing the topsides and leaving an exclusion zone around the jackets would have the least impact on the ecosystem. However, you run the risk of marine collisions, occupation (and hence accidents) by fishermen, and large parts falling off as the condition starts to degrade.

The "safest" solution is probably to cut the jackets back to, say 15 - 20m below lowest astronomical tide (depending on the draft of the vessels in the area), but then you'd sacrifice all the plant and animal life that grows in the top few meters of the water column - and there's a lot of it.

That's very interesting Shane. I thought that the drilling rigs did sit on the sea bed, because when they started the North Sea drilling they had a lot of trouble because of the depth. There always seems to be a lot of sea life associated with wrecks, so it makes sense that drilling rigs have the same effect. As you say, the problem is what to do with the top to minimise loss of ecosystem and maximise safety.

Most drill rigs are jack-ups, which means that they sail (or, more often, are towed) to the drill location and then lower legs down to the sea floor to jack themselves into a stable position clear of the water. When they've finished drilling, they jack the legs back up again and move onto the next job. Jack-ups typically operate in water depths of up to 200 metres or so, although some can manage around the 300-metre mark.

In deeper waters, drill rigs will be floating units, either mounted on a shipping hull or on pontoons (like the one in the article that blew ashore).

A few production platforms that have a lot of wells will be installed with permanent drilling facilities on board. These are the exception rather than the norm, though.

Are the North Sea ones mainly jack ups Shane? I know when they first started there they were having to develop different rigs as the water was deeper than the Gulf of Mexico where they were used to drilling.

Mostly, I think. Until recently, jack-ups were limited to around 150 metres or so water depth, but the newer generation can now hit around the 300 mark.

Floating drilling rigs have been around for ages, so I'd imagine its the new, deeper-water jack-ups that you've heard of. I could, of course, be completely wrong You'll normally find that anything up to 150m is exclusively the realm of jack-ups, between 150 - 300m is a mix, and anything over 300m is exclusively floaters. Of course, with rig rates in freefall and units being cold-stacked all over the place, oil companies are spoilt for choice right now, so that might throw the dynamic a little - in shallower water, at least.